In the digital graphic arts, graphic objects are formed by pixels that are juxtaposed in close formation and at sufficient resolution so as to give the effect to the observer of continuous, smooth graphics. This is true regarding the formation of graphic symbols for display on a computer screen as well as for printing and plotting using suitable output devices. In all cases, symbols appear smooth but are actually constituted by multiple pixels. The more pixels that are used per unit area, the finer is the resolution of the resulting image and the more difficult it is to observe discontinuities between adjacent pixels. But the discontinuities are present all the same.
Normally, pixels are considered to be the smallest printable unit that forms the lowest common factor of all graphic symbols and effectively is constituted by a dot that may be displayed, printed or plotted. Since all dots forming a graphic symbol are identical as are the dots in different graphic symbols, known printing and display devices do not differentiate between pixels that are used to form different graphic symbols.
A hard copy of a graphic image comprising one or more graphics symbols may be scanned so as to form a digitized image that may be stored and processed digitally using a computer. When the graphic image contains text, it may further be required not simply to store the text graphically but to convert alphabetic characters to computer characters that may then be word-processed. This is done using Optical Character Recognition (OCR) software, which, put simply, recognizes different letters of the printed alphabet and converts text, letter by letter, to the appropriate character in the ASCII table.
This works well when text is clean and free of stains and other foreign markings that are indistinguishable to the OCR software and so give rise to errors in conversion. But when text is faded or damaged it is very more difficult if not impossible to convert printed text to computer-editable format using known OCR techniques; and it is frequently difficult if not impossible to identify a printed character that is damaged or partially missing.
U.S. Pat. No. 5,396,564 (Fitzpatrick et al.) issued Mar. 7, 1995 discloses a method of, and apparatus for, processing a color coded character to recognize the character being examined by an OCR device. The color coded character comprises a predominate color associated with said character distinguishable by humans, and a non-predominate color associated with the character and non-distracting to humans, but distinguishable by a color scanner. This allows the non-predominate color of a character to be used as the sole criteria for recognizing the character. Thus, for example, “a” may be printed red, “b” may be printed blue, and “c” may be printed yellow. It is stated that color coding OCR eliminates the data storage and computer processing requirements of geometric OCR by eliminating shape processing. However, it requires that the OCR software know in advance the coding scheme being employed.
It would clearly be an advantage if graphic symbols were encoded in such a manner as to allow accurate decoding for example by OCR software even when the printed symbols are only partially legible and without the need for the OCR software to know in advance the coding scheme being employed.